This invention relates to a rotary fluid pump, and more particularly, to a type thereof which prevents a drive shaft from axial displacement. A conventional rotary fluid pump includes a stator housing having a generally cylindrical bore extending therethrough and a pair of end heads assembled at the opposite ends of the housing to cover the end heads of the bore and form a cavity. Each end head has a recess therein contiguous with the bore and a drive shaft journalled in at least one of the end heads and extending into the interior of the cavity eccentrically relative to the wall of the bore. A rotor is mounted on the drive shaft within the cavity, and a pair of side plates disposed one between each end of the stator housing and the adjacent end head divide the cavity into a pair of end chambers defined by the end head recesses and the plate. A plurality of vanes are slidably disposed in the rotor along the radial direction thereof to permit intake, compression and discharge of a fluid in cooperation with the rotor chamber by the radially outward movement of the vanes.
According to this type of device, inner peripheral surfaces of the side plates are required to be in contact with the side faces of the rotor to maintain the seal therebetween during rotation of the rotor. However, in this type, no special means is provided to prevent axial displacement of the drive shaft and the rotor merely engages the drive shaft by a spline or key. Therefore, the rotor may accidentally be moved along the axial direction thereof.
If the side plates follow the rotor movement, the seal between the side plates and the end faces of the rotor can be maintained. However, in fact, the side plate cannot sufficiently follow the axial movement of the rotor, so that it would be rather difficult to maintain seal between the side plates and the end faces of the rotor during such movement.